Mahasi walking meditation noting precision

When being mindful in Mahasi walking meditation, should the meditator walk very slowly in order to get time enough to fit the noting in? What should the meditator's attitude be if they skip a mantra note? Should one strain hard to get the prechosen mantra note right? How should one approach mistakes? What kind of concentration is needed? Is it enough to just be mindful with superficial concentration or must a high degree of concentration be developed? With momentary concentration, can the meditator get stuck to an object like with non-momentary concentration? What would right-concentration be with this kind of walking meditation practice?